I agree with Hotrod on this one. I don’t think you should go off “top speed” or “speed”, you should go off of Engine RPM as there are less variables (rearend gears, transmission, tire size, etc.).

Example: my 216 (3 speed & 3.55 gears) runs at roughly 3200-3300 RPMs at about 70 MPH (my Speedo is slightly off)

Chris

1951 Chevy pickup 3100
In the Stovebolt Gallery
Discussion in the DITY